- Patch #1651010 by pounard: HttpKernel patch introduces ob_flush() related...

- Patch #1651010 by pounard: HttpKernel patch introduces ob_flush() related PHP warnings on my environement, potential patch and performance improvement.

core/lib/Drupal/Core/EventSubscriber/RequestCloseSubscriber.php

@@ -41,7 +41,17 @@ public function onTerminate(PostResponseEvent $event) {
       drupal_serve_page_from_cache($cache);
     }
     else {
-      ob_flush();
+      // This listener will be run in all cases, including when sending an HTTP
+      // redirect code. In this particular case, PHP output buffer has not been
+      // initialized yet and won't be, calling the ob_end_flush() method would
+      // throw PHP warnings.
+      // See http://www.php.net/manual/en/function.ob-end-flush.php#42979
+      while (ob_get_level() > 0) {
+        // Using ob_end_flush() instead of ob_flush() will close the output
+        // buffer. This means that potential later errors won't get to the user
+        // and the HTTPd might release the connection sooner.
+        ob_end_flush();
+      }
     }
 
     _registry_check_code(REGISTRY_WRITE_LOOKUP_CACHE);